Our directory of things of interest

University Directory

Saving Nemo

Clown fish hiding in colorful anemone Clown fish hiding in colorful anemone Tanya Puntti/Shutterstock
27 May
2016
Bleaching sea anemones put clownfish species at risk

Disney’s Finding Nemo made the clownfish a household name, or species even, and drew special notice to its sea anemone home. ‘Ah-ah-ah, you forgot to brush,’ says Nemo’s overprotective father in the excitement of the hero’s first day of school, ‘do you want this anemone to sting you?’

By brushing up against the tentacles of sea anemone, clownfish maintain their immunity to its sting. It is a relationship from which both creatures benefit as ‘obligatory symbionts’, whereby they depend on each other for survival: the clownfish keeps its host clean of harmful invertebrates in return for shelter from predators. It is also a relationship that is being tested, as seas warm and anemones are impacted by more frequent bleaching events.

‘Broadly, if bleaching incidents continue to increase in frequency there is a risk to species survival,’ says researcher Danielle Dixson of the University of Delaware, who has been studying how clownfish behave towards bleaching. ‘Unfortunately our research has shown that bleaching does not break the symbiotic relationship between them.’ Unfortunate, because a bleached anemone is less safe to live in – they increase the chances of being eaten.

shutterstock 141022417Clownfish in bleached host sea anemone (Image: Levent Konuk)

Why are clownfish so stubborn to relocate? ‘Clownfish are behaviourally linked to one or a few particular anemone species for a home,’ says Dixson referring to the fact that 28 species of clownfish each have a preferred host out of ten species of anemone. ‘This limits their ability to acclimate if an entire reef bleaches.’

She tested this behaviour in the lab, offering different clownfish species a choice between a bleached and healthy version of their ideal host. In every case, the fish successfully chose the healthy option, demonstrating that they can detect bleaching. However, when deciding between a bleached version of their preferred host and a non-bleached version of a less-preferred host, they would stick with their preferred, bleached anemone. In other words, in sickness and in health, a clownfish will always choose its parter species as a host.

Out of the lab, it is even harder to up sticks and move in to another host as other anemones are usually spoken for and clownfish schools are restricted by a complex hierarchical system. Though they are all born male, clownfish are sequential hermaphrodites, which means the largest becomes female and second-largest its reproductive mate. The queue to reproduce is in size order. ‘Clownfish can live for decades,’ says Dixson. ‘Imagine if you waited 20 years for your chance to be reproductive, it’s a big deal if someone jumps the line and breaks the order. It’s not like they can just go to the next anemone and be accepted – they are aggressive when it comes to protecting their place.’

Related items

NEVER MISS A STORY - Follow Geographical on Social

Want to stay up to date with breaking Geographical stories? Join the thousands following us on Twitter, Facebook and Instagram and stay informed about the world.

More articles in NATURE...

Geophoto

Photography competition, Earth Photo, returns for the third year with…

Oceans

A new study reveals the process behind the strange phenomenon…

Wildlife

Hunting is a topic that attracts polarised viewpoints. But as…

Oceans

A compilation of 50-years worth of data on human activity…

Wildlife

From the US to the Mediterranean, herds of goats are…

Wildlife

Meet the 2020 Whitley Award winners

Wildlife

Protecting the most famous members of the animal kingdom may…

Climate

With Milan announcing an ambitious new plan to reduce air…

Wildlife

Loss of tourism revenue is having a worrying impact on…

Oceans

Researchers studying marine heatwaves in the northeast Pacific, known as…

Wildlife

The notion that the Covid-19 pandemic all began because one…

Energy

The price of oil is plummeting – Angus Parker takes…

Geophoto

With so much to see on our doorsteps, this is…

Wildlife

A new decade-spanning study, in which the longest migration of…

Climate

Marco Magrini analyses the implications of the COP26 delay

Climate

Covid-19 has forced us to reduce destructive atmospheric behaviours and…

Wildlife

Recruiting armies of albatrosses could enable the detection of illegal…

Nature

What better time to get reading? We’ve collected some of…